1. Field of the Invention
The present invention pertains to a chemical-mechanical polishing pad structure and composition which enable polishing uniformity. The polishing pad structure provides a means for feeding polishing slurry, reactive etching reagent, heat transfer medium (cooling fluid), lubricant, or combinations thereof to the surface of the polishing pad as well as a means for holding such slurry, etching reagent or other fluid materials upon the pad surface.
2. Brief Description of the Background Art
Chemical-mechanical polishing has been used for more than twenty-five years as a technique for polishing optical lenses and semiconductor wafers. During the past ten years, chemical-mechanical polishing has been developed as a means for planarizing interlevel dielectrics and for removing conductive layers within integrated circuit devices as they are fabricated upon various substrates. In fact, chemical-mechanical polishing is currently viewed by many semiconductor technologists as the most promising method for the global planarization, and as necessary to enable the fabrication of integrated circuit devices having dimensions below 0.35 .mu.m. Research is now targeted on ways to better understand and control the subtle interactions between the surface to be planarized, the polishing pad, and the chemical composition used to aid in the polishing (typically a slurry containing abrasive or reactive particulates).
The present invention pertains to a polishing pad structure and composition which enables polishing uniformity. As a backdrop for the significance of the present invention, it is helpful to review background art pertaining to polishing pads of the kind generally used within the integrated circuit fabrication industry.
U.S. Pat. No. 4,138,228 to Hartfelt et al., issued Feb. 6, 1979, describes a polishing pad consisting essentially of platelets of a polymer and an inorganic polishing abrasive of an average particle size of less than 10 microns, wherein the platelets form a microporous sponge-like polymer matrix which is liquid absorbing, and essentially all of the abrasive particles are unencapsulated and carried upon (affixed to) the surfaces of the platelets. Preferably the polymer is bonded weakly to the polishing abrasives, whereby a controlled release of polishing abrasive from the polymer occurs during polishing.
U.S. Pat. No. 4,728,552 to Wilmer Jensen, Jr., issued Mar. 1, 1988, discloses a poromeric polishing pad comprising a felt sheet of fibers impregnated with a microporous elastomer. The polishing pad is constructed such that the majority of fiber ends adjacent to the work surface of the pad form an angle of between about 45.degree. and about 135.degree. with respect to the surface to be polished. Preferably the fibers have an orientation substantially perpendicular to the work surface.
U.S. Pat. No. 4,841,680 to Hoffstein et al., issued Jun. 27, 1989, describes a polishing pad material having a cellular polymeric layer (typically a polyurethane elastomer) containing elongated cells (formed within the polyurethane elastomer by the process used to coagulate the elastomer from a solution). The skin of the cellular polymeric layer is removed to expose the elongated cells which are used to hold the slurry on the surface of the polishing pad during polishing operations.
U.S. Pat. No. 4,927,432 to Budinger et al., issued May 22, 1990, discloses a polishing pad material produced by reinforcing a conventional porometric material (such as polyurethane, formalized polyvinyl alcohol, polycarbonate, and polyureas) with a fibrous network such as a felted mat of polyester fibers. The resin is coalesced among the fibers, preferably by heat treatment, to increase porosity and hardness of the polyurethane as well as increasing surface activity of the resin. Photomicrographs of the pad material show the fibers to be generally randomly oriented within the porometric material.
U.S. Pat. No. 5,020,283 to Mark E. Turrle, issued Jun. 4, 1991, describes a polishing pad having a face shaped by a series of voids. The voids are substantially the same size, but the frequency of the voids increases with increasing radial distance from the center of the pad. This void pattern is said to provide a nearly constant surface contact rate at the workpiece surface during polishing. The voids are preferably depressions or grooves, although it is said the voids could be holes extending entirely through the pad. No material or method of construction is called out for the polishing pad; however, based on the drawings, the voids are machined into the surface of the pad.
U.S. Pat. No. 5,212,910 to Breivogel et al., issued May 25, 1993, discloses a composite polishing pad which comprises a first support layer of elastic material (attached to the pad support table), a second and intermediate stiff layer which is segmented into individual sections physically isolated from one another in the lateral dimension, and a third spongy layer optimized for slurry transport. Each segmented section of the second layer is resilient across its width, yet cushioned by the first layer. The physical isolation of each section, combined with the cushioning of the first layer of material is said to create a "bedspring" effect which enables the pad to conform to longitudinal gradations across the surface to be polished. Preferably the first layer is a silicone sponge rubber or foam rubber, the second layer is a composite fiberglass epoxy material, and the third layer composition is not specifically identified other than by the name "SUBA 500" (a product of Rodel, Inc. of Newark, Del.).
U.S. Pat. No. 5,329,734 to Chris C. Yu, issued Jul. 19, 1994, describes a polishing pad having a first region near the edge of the pad and a second region located interior to the first region. The second region has a plurality of openings or a larger average pore size compared to the first region. The openings can be depressions within the surface of the pad or channels which pass completely through the pad. Pores are distinguished from openings because pores are said to be formed during the reaction to produce the polymeric polishing pad material while openings are formed within the pad after the polishing pad material has been formed. The depressions or openings are said to be fabricated using laser ablation or mechanical machining techniques. The-polishing pad is fastened to an underlying substrate using an adhesive. Yu describes the openings, which provide slurry-holding voids, as occupying from between about 5 and about 50% of the surface area within the portion of the polishing pad in which such openings are present.
All of the above polishing pads seek to provide a means for holding a polishing compound or slurry uniformly across the surface of the polishing pad. Some of the polishing pads provide fibers or abrasive materials within the pad itself to aid in the polishing operation. The present invention provides a means for holding a slurry uniformly across the surface of a polishing pad, provides the capability for feeding polishing slurry, reactive etchant material, cooling fluid and/or lubricant through the pad to the surface of the article being polished, and may provide the equivalent of fibers which act as abrasive agents, depending on the polishing pad materials of construction.